A battery includes a positive electrode, a negative electrode, and a separator. The negative electrode forms a honeycomb core. The honeycomb core includes a first face, a second face, a partition, and a circumferential wall. The second face faces the first face. The partition is formed between the first face and the second face. The partition extends in a grid pattern to separate a plurality of hollow cells. The circumferential wall surrounds a circumference of the partition. The separator includes a first layer and a second layer. The first layer covers at least part of the partition. The second layer covers at least part of the first face and the second face. The positive electrode includes a first region and a second region. The first region is inserted in the hollow cells. The second region extends outwardly beyond the second layer of the separator.